Linear cathode high-energy electron beam apparatus

ABSTRACT

A linear cathode high-energy electron beam generating apparatus of the multi-stage acceleration type comprising a linear cathode for emitting a planar electron beam, and a plurality of cylindrical electrodes disposed one into another so as to surround the path of the planar electron beam, whereby the height of the generating apparatus is greatly reduced as compared with known electron beam apparatus.

United States Patent [191 Arakawa et al.

1 1 LINEAR CATHODE HIGH-ENERGY ELECTRON BEAM APPARATUS [75] Inventors: Kazuo Arakawa, Toyonaka; Koichi Shinohara, Osaka; Yasuhiro Shimizu, Toyonaka, all of Japan [73] Assignee: Matsushita Electric Industrial Co.,

Ltd., Osaka, Japan [22] Filed: June 4, 1971 211 Appl. No.: 150,018

[30] Foreign Application Priority Data June 8, 1970 Japan 45-49686 [52] US. Cl 313/299, 313/74, 313/83 [51] Int. Cl H0lj 29/46, HOlj 33/04 [58] Field of Search 313/356, 74, 299, 300

[56] References Cited UNITED STATES PATENTS 6/1934 Kuntke 313/356 X 12/1935 Thompson 313/356 X H/GH VOL 7146f POWER CONT/POL VOL 746E June 11, 1974 2,030,396 2/1936 Randall 313/356 X 2,111,231 3/1938 Ardenne 313/300 X 2,558,021 6/1951 Variar et a1 313/356 X 2,708,262 5/1955 Dwork 313/74 X 2,887,599 5/1959 Trump 313/74 3,218,431 11/1965 Stauffer.... 313/356 X 3,320,475 5/1967 Boring 313/356 X 3,411,035 11/1968 Necker et a1. 313/356 X Primary Examiner-John K. Corbin Attorney, Agent, or FirmStevens, Davis, Miller &

Mosher 5 7 ABSTRACT A linear cathode highenergy electron beam generating apparatus of the multi-stage acceleration type comprising a linear cathode for emitting a planar. electron beam, and a plurality of cylindrical electrodes disposed one into another so as to surround the path of the planar electron beam, whereby the height of the generating apparatus is greatly reduced as compared with known electron beam apparatus 4 Claims, 4 Drawing Figures I 30 HEATER POWER ,v CONT/POL 29) VOL 72765 26 23 24 PUMP LINEAR CATHODE HIGH-ENERGY ELECTRON BEAM APPARATUS This invention relates to a linear cathode high-energy electron beam generating apparatus, particularly to such a device suitable for generating a stationary (nondeflected) and planar electron beam of a high energy level in the order of 100 to 500 KeV.

The main object of this invention is to provide an electron beam generating apparatus of the abovementioned type which is improved in structure and compact in size.

Electron beam generating apparatus known by such names as the Cockcroft generator, Van de Graaff accelerator and resonant transformer type accelerator are used, among others, for irradiating polymeric or other materials with electron beam to change the properties of the material.

These accelerators are provided with a point type emitter. The linear electron beam emitted from the emitter is accelerated by an acceleration field and then fanned out by a magnetic or electric deflection means to evenly irradiate an object.

Recently, an electron beam generating apparatus based on a principle different from that for the abovementioned accelerators has been developed. The new beam generating apparatus is provided with a linear emitter and may be called a linear cathode accelerator. With such a beam generating apparatus, a planar electron beam projected from the linear emitter is directed to an object after being properly accelerated. Thus, beam deflecting and focusing means are dispensed with, and a compact and inexpensive beam generating apparatus can be obtained.

l-Iereunder, description will be given with reference to the accompanying drawings, in which:

FIGS. 1 and 2 are cross-sections of known electron beam generating apparatus shown with block diagrams of energizing circuits;

FIG. 3 is a cross section of an embodiment of the electron beam generating apparatus of this invention; and

FIG. 4 is a bottom view of the assembly of electrodes in the generating apparatus shown in FIG. 3.

Referring to FIG. 1 which shows a cross section of the recently developed and known beam generating apparatus as mentioned above, an evacuated envelope 2 is provided with an irradiation window 1 made of a thin film of aluminum or titanium. Within the envelope 2, there are provided a linear cathode 3 and a control electrode 4 which are disposed so as to direct an electron beam emitted from the cathode 3 toward the window 1; a high voltage is applied between the cathode 3 and the envelope 2, the latter serving as a grounded anode, to accelerate the electron beam. Thus a planar flux of electrons are projected through the window 1. Other parts and components shown in FIG. 1 are a high voltage source 5 for supplying the acceleration voltage, a power source 6 for heating the linear cathode 3, a voltage source 7 for the control electrode 4, insulating bushings 8, and a vacuum pump 9 for evacuating the envelope 2.

With the above-described beam generating apparatus, however, the energy level of the emitted electron beam is limited to the order of 100 KeV, due to the dielectric breakdown of the vacuum space. As is well known, the dielectric breakdown voltage of a vacuum space is not proportional to the distance between electrodes, but tends to approach a certain constant value because of so-called total voltage effect. This tendency is especially marked in a vacuum envelope which is continuously evacuated during operation, the practical ceiling value of breakdown voltage of the vacuum being the order of KeV.

In order to provide higher acceleration voltage and to thereby generate an electron beam of higher energy level, a multi-stage acceleration system based on the principle similar to that of the Van de Graaff accelerator has been proposed.

FIG. 2 shows an electron beam generating apparatus of such a type, in which the multi-stage acceleration arrangement is composed by stacking alternately acceleration electrodes 10 and insulating spacers 1 1, and providing means such as a voltage divider 12 for applying appropriate acceleration voltages to the respective acceleration electrodes. Also shown in FIG. 2 are a linear cathode 13, a control electrode 14, a top panel 15, a bottom panel 16, an irradiation window 17 provided in the bottom panel 16, a high voltage source 18 for supplying the acceleration voltage, a power source 19 for supplying heating power to the linear cathode 13, a voltage source 20 for the control electrode 14, insulating bushings 21, and a vacuum pump 22.

In the above arrangement, the insulating spacers 11 have the shape of oblong rectangular frames. The length of the frame can be as long as l m or even 2 m. It will be noted that to construct a hermetic structure by stacking such long frames and electrodes is practically very difficult. A further disadvantage with the above structure is the fact that the location of the outlet to vacuum pump is restricted to the grounded bottom panel 16 which is provided with the window 17 and should preferably be free from any obstructive protrusion. An alternative measure to avoid this difficulty is to mount the vacuum pump on the high potential to panel 15 and provide a special power supply insulated against ground for energizing the vacuum pump. However, such an arrangement is impractical in actual construction.

these difficulties with the known electron beam generator are overcome by this invention.

In order to achieve the above object, the electron beam generator of this invention comprises a linear cathode for emitting a planar electron beam, and a plurality of cylindrical electrodes disposed planar electron beam.

Referring to FIG. 3 which schematically shows the essential structure of the electron beam generating apparatus of this invention, there are provided a linear cathode 23, a control electrode 24, and a plurality of cylindrical acceleration electrodes 25 disposed so as to surround the path of the planar electron beam emitted from said linear cathode 23. The electrodes are spaced so as to ensure dielectric insulation between one another against designed potential differences therebetween. The lengths and the positions of the acceleration electrodes 25 are set considering the electrooptical requirements for a proper acceleration of the electrons. Though the transverse sections of the cylindrical electrodes 25 may be of any suitable shape, rectangles as shown in FIG. 4 are typical and are the most favorable shaped in view of fabrication and the electro optical conditions. The outermost cylinder 26 serves as the grounded anode and also as the body of the enclosure of the generating apparatus. In the bottom of the enclosure is provided an electron transmissive window 27 through which the electron beam is projected. The cylindrical acceleration electrodes are supported by insulating members 28 at the top of the enclosure 26, and secured to the insulating members 28 in a hermetic manner. For example, oblong ceramic blocks 28 are inserted between the end portions of cylindrical electrodes 25 and the assembly is hermetically sealed with epoxy adhesive according to known sealing techniques.

Other components and means shown in F IG. 3 are a high voltage source 29 for supplying the acceleration voltage, a power source 30 for heating the cathode 23, a voltage source 31 for the control electrode 24, resistors 32 for dividing the high voltage, a vacuum pump 33, a top panel 34, and sealed insulating bushings 35.

It will be understood that the linear cathode 23 need not necessarily be a single filament or strip, but it may be a coil or a group of linearly disposed filaments or coils or a combination thereof.

An electron beam generating apparatus according to this invention which has a linear cathode of 2 m long and two rectangular cylindrical acceleration electrodes 25 besides the anode 26 and which is capable of generating electron beam of 200 KeV, 30 mA, has dimensions of 2,500 mm X 250 mm X 250 mm, the installation height being approximately one third of that of a typical Van de Graaf accelerator of corresponding capacity.

Further, an electron beam generating apparatus of 500 KeV class can be constructed according to this invention by adding further acceleration electrodes.

What we claim is:

1. A linear cathode high-energy electron beam apparatus for projecting a planar electron beam outside an electron transmissive window of an evacuated envelope, comprising a linear cathode fixed to a top panel for emitting a planar electron beam of an elongated rectangular cross section, a control electrode disposed adjacent to said linear cathode, the longitudinal direction of said control electrode being the same as the longitudinal direction of said linear cathode, and a plurality of tubular acceleration electrodes disposed substantially one inside another, said linear cathode and said control electrode being disposed substantially inside the innermost acceleration electrode, said acceleration electrodes having their respetive longitudinal lengths different from one another and their respective central axes substantially perpendicular to the longitudinal direction of said linear cathode, said acceleration electrodes being opened at respective one end portions to pass therethrough the planar electron beam from said linear cathode, the respective other end portions of said acceleration electrodes having interposed insulating members between said top panel and the outermost acceleration electrode and being hermetically secured thereto, and the outermost acceleration electrode serving as the evacuated envelope together with said top panel and said insulating members and having at the opened one end portion the electron transmissive window aligned perpendicular to the central axes of said acceleration electrodes.

2. A linear cathode high-energy electron beam apparatus according to claim 1, wherein the transverse sections of said cylindrical electrodes are rectangles.

3. A linear cathode high-energy electron beam apparatus according to claim 1, wherein said cylindrical electrodes are concentrically disposed.

4. A linear cathode high-energy electron beam apparatus according to claim 1, wherein the respective longitudinal lengths of said acceleration electrodes are gradually reduced from the outermost acceleration electrode to the innermost acceleration electrode. 

1. A linear cathode high-energy electron beam apparatus for projecting a planar electron beam outside an electron transmissive window of an evacuated envelope, comprising a linear cathode fixed to a top panel for emitting a planar electron beam of an elongated rectangular cross section, a control electrode disposed adjacent to said linear cathode, the longitudinal direction of said control electrode being the same as the longitudinal direction of said linear cathode, and a plurality of tubular acceleration electrodes disposed substantially one inside another, said linear cathode and said control electrode being disposed substantially inside the innermost acceleration electrode, said acceleration electrodes having their respetive longitudinal lengths different from one another and their respective central axes substantially perpendicular to the longitudinal direction of said linear cathode, said acceleration electrodes being opened at respective one end portions to pass therethrough the planar electron beam from said linear cathode, the respective other end portions of said acceleration electrodes having interposed insulating members between said top panel and the outermost acceleration electrode and being hermetically secured thereto, and the outermost acceleration electrode serving as the evacuated envelope together with said top panel and said insulating members and having at the opened one end portion the electron transmissive window aligned perpendicular to the central axes of said acceleration electrodes.
 2. A linear cathode high-energy electron beam apparatus according to claim 1, wherein the transverse sections of said cylindrical electrodes are rectangles.
 3. A linear cathode high-energy electron beam apparatus according to claim 1, wherein said cylindrical electrodes are concentrically disposed.
 4. A linear cathode high-energy electron beam apparatus according to claim 1, wherein the respective longitudinal lengths of said acceleration electrodes are gradually reduced from the outermost acceleration electrode to the innermost acceleration electrode. 